This invention is concerned with the improvement of the detergent and antioxidant ability of a particular class of compounds which have been taught in the prior art as highly effective detergent additives for lubricating oils. These compounds, so-called "over-based" metal derivatives of phenolic-type compounds, are described in U.S Pat. No. 2,680,096.
U.S. Pat. No. 2,680,096 teaches basic calcium phenates which contain a ratio of equivalents of calcium to equivalents of phenol which is substantially greater than that of the "normal" sulfurized calcium phenates. They contain up to 200 mole percent of calcium per mole of phenol. The prior art has recognized that the excess calcium contents of these detergent additives makes them more effective detergent additives than the normal basic sulfurized calcium phenates.
The conventional procedure for forming the overbased sulfurized calcium phenate salts requires a considerable excess of a calcium compound which can be in the form of calcium oxide or calcium hydroxide. In the prior art it has been found that neutralization of the phenolic compound in the presence of a polyhydroxy organic compound provides a product containing a higher percentage of metal than does the product produced in the absence of the polyhydroxy organic compound. This procedure is described in U.S. Pat. No. 2,680,096.
U.S. Pat. No. 2,680,096 teaches that treatment of phenol with an excess amount of a neutralizing agent in the presence of a minor amount of a polyhydroxy organic compound such as a low molecular weight polyhydric alcohol having in the range 2 to 6 carbon atoms results in a product with increased metal content. Less neutralizing agent is accordingly required to obtain a product with a given metal content. The polyhydroxy compounds used can include ethylene glycol, propylene glycol; butanediol-2,3; pentanediol-2,3; and 2-methylbutanediol-3,4. Because of the higher yield of product obtained, ethylene glycol is the preferred solvent.
Referring again to U.S. Pat. No. 2,680,096, it is seen that the basic sulfurized calcium phenates are prepared from either normal calcium phenates or phenols as starting materials. When phenols are used as the starting material, they are treated with calcium oxide or hydroxide to form the desired normal calcium phenate which are then treated further with calcium oxide or calcium hydroxide in the presence of glycols to form the sulfurized basic calcium phenates. The phenols can also be treated with calcium oxide or hydroxide in amounts to form the sulfurized basic calcium phenates directly by reaction of the phenols with calcium oxide or hydroxide and sulfur in the presence of glycols.
Other investigators in the sulfurized metal phenate field have formulated various types of compounds. Typical investigations are disclosed in U.S. Pat. Nos. 2,680,097; 2,766,291; 3,036,971; 3,178,368; 3,801,507 and others.
U.S. Pat. No. 3,801,507 teaches that sulfurized metal phenates having improved antioxidant activity and dispersancy are prepared by reacting an alkaline earth metal base with a sulfurized alkylphenol and having an average sulfur-to-metal atom ratio between 1 and 4. The compounds are prepared in a two step reaction procedure in which 1.0 to 5 moles of sulfur and from 0.05 to 1.5 moles, preferably 0.2 to 1.0, mole of alkaline earth metal base are contacted in a first step with each mole of an alkylphenol having from 8 to 35 carbons in the alkyl group. The contacting is conducted in the presence of 0.1 to 4 moles, and preferably from 0.2 to 1 mole, of a mutual solvent having solvency for the alkylphenol and alkaline earth metal base per mole of alkylphenol. In a second step, the sulfurized reaction product above is contacted with zero to 1.45 moles of additional alkaline earth metal base and 0.5 to 4 moles of mutual solvent per mole of original alkylphenol under conditions conducive to the formation of the sulfurized alkaline earth metal phenate product.
Hydrogen sulfide and water are evolved in both the first and second steps of the U.S. Pat. No. 3,801,507 process. The patent also teaches, colum 4, lines 66-70, delayed removal of the hydrogen sulfide and water vapor encourages the oxidation of some of the mutual solvent, such as ethylene glycol, to glycolic acid, oxalic acid, etc., which in turn react with the metal base and reduce the base reserve of the product. The alkalinity value (ASTM Test D-2896) of the sulfurized metal phenate, hereinafter referred to as total base number (TEN) ranges from 40 to 200 mg KOH/gram and more usually from 90 to 150 mg KOH/gram.
It has now been found in accordance with the present invention that the effectiveness of the basic sulfurized calcium phenates can be substantially increased in a batch or continuous process wherein formation of neutral calcium compounds is reduced to a minimum by the invented method of reacting the reaction compounds and the sulfur/calcium/glycol/alkylphenol mole ratios. The reaction between the alkylphenol, glycol and calcium compound in a prereaction step is critically controlled as to temperature and reaction time. Sulfur is not added to the reaction mixture until the glycol has formed a reaction intermediate with the alkylphenol and calcium compound.
In the prior art, it is taught to react a mixture of a calcium compound, sulfur and a polyhydroxy compound such as ethylene glycol and an alkylphenol to prepare a sulfurized calcium alkylphenate. For example, U.S. Pat. No. 2,680,096 teaches that it is essential (column 2, lines 32-35) the elemental sulfur be present along with the calcium oxide or calcium hydroxide, glycol and alkylphenol. U.S. Pat. No. b 3,801,507 teaches that the three reactants of sulfur, alkylphenol and alkaline earth metal oxide or hydroxide are brought together in the presence of a mutual solvent which can be glycol. U.S. Pat. No. 3,801,507 teaches that the concentration of alkylphenol, alkaline earth metal base, sulfur and mutual solvent is not important and can vary with selection of reactants and process conditions, etc.
Contrary to the teachings of the prior art, it has been found that formation of a neutral calcium compound is promoted in a reaction mixture when a calcium compound is heated in the presence of glycol and sulfur. The presence of the neutral calcium compound, which can be calcium oxalate, reduces the effectiveness of the sulfurized calcium alkylphenate as a lubricating oil additive in preventing engine deposits and as an antioxidant. It has also been found that critical mole ratios of lime, glycol and alkylphenol minimize the formation of undesirable glycol complexes. Formation of neutral calcium compounds and these undesirable complexes from glycol wastes materials and lessens quality control of the final lubricant additive and the lubricating oil containing the additive.
Accordingly, in the prior art there was no recognition that a process which reacted the glycol with the calcium compound and alkylphenol in critical mole ratios in the absence of sulfur to form an intermediate would reduce the presence of a neutral calcium compound in the final product, the presence of which could be monitored by infrared analysis.